Serious aircraft accidents have been caused by lack of complete and immediate information to pilots concerning positions of aircraft on runways and especially concerning the amount of runway remaining until the end in the direction of aircraft travel. Knowledge of the length of the remaining runway is imperative for good safety during takeoff and during landing.
In takeoff procedures there are two important reasons why a pilot must know the distance to the end of the runway in the direction of aircraft travel. All aircraft have minimum runway lengths which are usable under conditions of loading. It is important that a pilot be apprised of the runway length or the length of runway between his position and the distant end in the direction of aircraft travel so that the pilot may know whether the runway length is sufficient to meet minimum takeoff requirements.
During the takeoff acceleration, it is sometimes necessary or desirable to abort a takeoff. Control failures or power losses or indications of such failures or losses may suggest danger in a continued takeoff. At varied increments of velocity each aircraft has a safe stopping distance according to loading and runway surface characteristics. It is important at all times during takeoff that a pilot know his exact position on the runway so that he can quickly consider the speed of the aircraft and the factors of weight and runway conditions in deciding whether there is sufficient distance left for aborted takeoff procedures. Bad accidents have recently been caused by pilots' believing there to be more runway remaining than was actually remaining at the beginning of their takeoff aborting procedures.
In landing an aircraft, especially in periods of low visibility, it is sometimes difficult for a pilot to tell exactly where the touchdown point was on a runway strip. Thus, the pilot may not know the distance remaining on the runway. Often, emergency braking procedures will bring the craft to a rapid and safe stop even though passenger discomfort and slight equipment damage may result. A pilot is hesitant to use those procedures of fast stopping unless he is absolutely sure that such procedures are required. In low visibility conditions, when a pilot flies over the end of the runway and does not see the touchdown end and cannot see the distant end, under present conditions he has no reference to indicate the remaining distance to the end of the runway.
There is a great need both in takeoff procedures and in landing procedures to have the actual distance remaining on a runway marked and readily visibly accessible to a pilot.
Some runway marking devices have been proposed. However, due to complexities of the structure of those devices and due to their high equipment and installation costs, the devices have not been used. However, it is extremely important that any device erected along a runway be readily collapsible so as not to present an unnecessary danger to aircraft using the runway. Marking devices which have been collapsible have been so expensive to construct and to use as to make them of little value for widespread and intensive use on runways.
Marking devices have been proposed to indicate by illumination particular sections of runways. Such devices have suggested the use of varied colored lighting creating cones of light colors which indicate position on a runway. Such systems have been expensive to install, confusing in their use and incapable of equal use in opposite senses of direction such as required by wind changes.